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Describe uveal coloboma and the congenital anomalies of the iris.

Ophthalmology · 3rd Professional

Uveal Coloboma

A coloboma is a congenital defect resulting from failure OF closure of the embryonic (choroidal, optic) fissure, which normally closes between the 5th and 7th week of gestation.

Because the fissure lies inferonasally, a typical coloboma is always inferonasal — and this single anatomical fact identifies it. A defect in any other position is an atypical coloboma, arising by a different mechanism
Structures affected, in the order the fissure runs — the iris, giving the classical "keyhole" or pear-shaped pupil pointing downward and inward; the ciliary body, with absent zonules causing lens notching and subluxation; the choroid and retina, seen as a white, well-defined, excavated area with pigmented margins through which the bare sclera is visible; and the optic disc

Congenital Anomalies of the Iris

Anomaly	Features
Aniridia	Near-total absence of the iris, with only a rudimentary stump visible on gonioscopy. Almost always bilateral. Caused by mutation of the PAX6 gene on chromosome 11p13. Associated with foveal hypoplasia (hence poor vision and nystagmus from birth), limbal stem cell deficiency with progressive corneal opacification, glaucoma in about half, and cataract. Critically: the sporadic form is associated with WAGR syndrome — Wilms tumour, Aniridia, Genitourinary anomalies and Retardation — so every child with sporadic aniridia requires genetic testing and renal surveillance by regular ultrasound for Wilms tumour
Corectopia	Displacement of the pupil from its normal position; may be congenital or follow trauma or iridocorneal endothelial syndrome
Polycoria	More than one pupil. True polycoria requires each pupil to have its own sphincter and react; most cases are pseudopolycoria, being simple iris holes
Persistent pupillary membrane	Remnants of the anterior vascular tunic of the lens, seen as fine strands arising from the collarette (not the pupil margin) and crossing the pupil. Very common, and almost always visually insignificant; requires no treatment
Heterochromia IRIDIS	Difference in colour between the two irides. Congenital — HORNER syndrome (the affected side lighter, and heterochromia indicates a congenital or early lesion), waardenburg syndrome, and naevus of Ota (the affected side darker). Acquired — FUCHS heterochromic iridocyclitis (lighter), siderosis from a retained iron foreign body (darker), and prostaglandin analogue eye drops (darker)
Albinism	Oculocutaneous or ocular; iris transillumination, foveal hypoplasia, nystagmus, photophobia, reduced acuity, and misrouting of the optic nerve fibres at the chiasm with abnormal visually evoked potentials
LISCH nodules	Multiple bilateral tan iris hamartomas; present in almost all adults with neurofibromatosis type 1 and a diagnostic criterion

Applied Aspects

An inferonasal iris defect is a coloboma; a defect anywhere else is atypical and suggests trauma, surgery or another mechanism
Examine the fundus in every iris coloboma; the visual prognosis depends entirely on whether the macula and disc are involved, and the iris defect itself matters little
Refer every child with sporadic aniridia for genetics and renal ultrasound; WAGR syndrome carries a real risk of Wilms tumour and the surveillance is lifesaving

All questions in Diseases of the Uveal Tract

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